This invention relates generally to dilatation devices and, more specifically, to balloon catheters having an essentially uniform outer diameter with a variable wall thickness of desire compliance and break pressure upon inflation.
In coronary balloon catheters, a continuous length of polymer tube is utilized to form a balloon. Typically, the balloon portion of the tube must be wrapped or folded to take up the slack of the balloon portion and to insure that the outer diameter of the wrapped or folded tube is sufficiently small to be insertable into blood vessels.
Factors to be considered when fabricating dilatation devices include: (a) minimizing the outer diameter (xe2x80x9cODxe2x80x9d) of the tube and/or the balloon portion to enable it to be passed easily through the desired vessels or organs of the body, (b) providing sufficient strength to the tube without undesired kinking, bending or twisting to enable it to be passed easily to the site of the occlusion being treated, and (c) insuring that the balloon, once inflated at the site of the occlusion, has a desired compliance and tensile strength to allow expansion in a controlled manner to a desired inflated diameter of the balloon, and to minimize the chance of bursting the balloon.
In the past, designs intended to accommodate some of these factors have included: (a) a double-layered balloon comprising an inner non-elastic balloon and an outer elastic balloon, as disclosed in U.S. Pat. No. 4,608,984; (b) an expandable and collapsible balloon reinforced by knitted fabric to insure that the balloon cannot expand beyond a predetermined diameter; (c) the use of high molecular weight polymer, such as polyethylene terephthalate (xe2x80x9cPETxe2x80x9d) polyester, to provide a bi-axially oriented, flexible polymeric balloon having a burst pressure of at least 200 psi and a radial expansion beyond the desired inflated diameter of less than 5% at 200 psi, as disclosed in U.S. Pat. No. 4,490,421; and (d) the use of fiberglass or shell wire fused over a polyurethane catheter to reinforce the tube at the beginning and ending of the thinned (balloon) portion. In addition, U.S. Pat. No. 5,348,538 discloses a method to make a (rigid polyurethane or PET) balloon catheter having a non-linear compliance curve formed by shrinking the balloon tube to a diameter below its original diameter. The resulting balloon catheter is said to be compliant if it exhibits a non-compliant compliance curve when expanded beyond its original diameter. U.S. Pat. No. 5,733,496 also discloses a method of stiffening a compliant polymer tube, upon manufacture thereof, by exposing the tube to e-beam radiation.
An important problem associated with conventional catheter balloon systems is that the balloon xe2x80x9cbag,xe2x80x9d even when wrapped or folded in order to minimize its diameter, possesses a larger outer diameter than that associated with the remainder of the catheter tube. Although tubing of non-uniform outer diameter is known in the tube extrusion field, as illustrated by the disclosures of U.S. Pat. No. 5,511,965, such non-uniform tube requires complicated mandrels and mechanical dies, making this application impractical in the balloon catheter field. Indeed, the larger diameter balloon portion poses a risk of difficulty in threading the tube into the occluded blood vessel during use. Therefore, there is a need for an easily constructed catheter balloon capable of unitary and integral construction having a uniform or near uniform outer diameter in order to provide relative ease of insertion into a blood vessel or body cavity.
Other uses for tubes with an expandable portion (balloon portion) of uniform OD relative to a less expandable portion (non-balloon portion) include gastroenterology catheters, urethral catheters, neurological catheters, endotrachial catheters, or peritonieal drains. In addition, such a tube has other potential applications of a medical or non-medical nature, wherein it might be desirable to thread a tube into a restricted size opening and then inflate the tube radially to that opening so as to either block the opening, reduce an obstruction or prevent the tube from being inadvertently withdrawn.
The term xe2x80x9cunitary constructionxe2x80x9d or xe2x80x9ccontinuousxe2x80x9d as used herein, when applied to an article of manufacture such as a balloon catheter tube, means an article of manufacture which is fabricated in a single piece, as opposed to an article of manufacture which is fabricated by the joining together of separate pieces. Thus, an article of unitary construction is seamless. Similarly, the term xe2x80x9cintegralxe2x80x9d as used herein, when applied to adjacent portions of an article, means that there is no joint, seam, or material boundary between the subject portions.
Further, the term xe2x80x9cpolymer tubexe2x80x9d refers to one which has memory either inherent or induced by some mechanical process such as stretching or preferably by crosslinking the material by radiation or heat.
Dilatation devices have a variety of uses in the medical field and in industrial and commercial applications where narrow areas must be dilated. The present invention discloses a device made from a continuous length of tube that overcomes the limitations of the prior art. Further, a method of forming these devices is disclosed.
In one aspect, the present invention relates to a dilatation device comprising a continuous length of polymer tube having an essentially uniform outer diameter with an integral expandable portion and a less expandable portion, said expandable portion having a wall-thickness less than that of said less expandable portion.
Preferably, the polymer tube is comprised of a polymer imparted with memory. Memory may be imparted in a variety of ways, including crosslinking by irradiating or heating the material. Ideal crosslinked polymers include crosslinked thermoplastic elastomers, crosslinked thermoplastic polymers, crosslinked polyamide polymers, crosslinked polyamide elastomer block co-polymers, crosslinked polyester elastomer block co-polymers, crosslinked thermoplastic polyurethane polymers, crosslinked polyethylene polymers, or crosslinked polyethylene co-polymers. Examples of suitable thermoplastic elastomers include a block co-polymer, a graft co-polymer, a blend of elastomers and thermoplastics, or an ionomer. Further, polyethylene terephthalate homopolyester polymers or polybutylene terephthalate homopolyester polymers may be suitable tube materials.
The crosslinking of the material may be performed by heat crosslinking in the presence of a heat-activated catalyst, such as an organic peroxide. Further, the crosslinking may be performed by photonic radiation, such as high energy electron beam particles, gamma radiation particles, UV radiation and combinations thereof. In addition, such crosslinking may require the presence of monomeric crosslinking agents such as allylic, methacrylic, or acrylic crosslinking monomers which are well known to those skilled in the art. The radiation dosage will depend on the material being used, but will generally range between approximately 0.1 and 250 MegaRads.
The present invention also relates to a preferred process to form the device described above, comprising manipulating a portion of a tube of polymeric material by:
(a) providing a tube with a memory of an original wall thickness, outer diameter and length;
(b) heating said tube;
(c) applying pressure to the interior of the tube to expand a portion of said tube to form a balloon of a desired shape and size, said portion have an original length;
(d) releasing the interior pressure and collapsing said balloon; and,
(e) simultaneously allowing said balloon to radially shrink while longitudinally restraining said balloon thereby manipulating the wall thickness of said balloon as it shrinks, said heated and shrunk balloon thereby forming an expandable portion in said tube.
There are many different ways to form the balloon in the tube which are well known to those skilled in the art. For example, the balloon may be formed in free air or in the presence of a mold. Further, the balloon may be formed by applying pressurized gas or fluids against the interior of the tube.
In one aspect of this process, the balloon is cooled before the interior pressure is released and the balloon is collapsed. The balloon is then reheated in a controlled manner before the expandable portion is radially shrunk.
In a preferred embodiment, the step of longitudinally restraining said portion is performed so as to create a finished tube with an overall length longer than that of the original tube and with a portion containing a thinner wall thickness than the original tube. While the balloon radially shrinks, the portion of the tube in which the balloon was formed is held at a length longer than the original length of said portion. The end result is a longer tube containing a portion with a thinner wall thickness as depicted in FIG. 1. Alternatively, said portion can be longitudinally elongated in a controlled manner during balloon shrinkage so create a tube that is substantially longer than the original tube and with substantially thinner walls.
The process described above results in a tube with an expandable portion and less expandable portion. When the tube is pressurized, the expandable portion inflates to form a balloon while the less expandable portion remains as a tube and does not inflate to form a balloon.
Accordingly, an objective of the present invention is to provide a dilatation device that has a minimal outer diameter (xe2x80x9cODxe2x80x9d) so as to be passed easily through narrow openings.
Another objective of the present invention is to provide a dilatation device that has sufficient strength but avoids kinking, bending or twisting and is therefore easily passed to the desired location, such as an occlusion being treated.
Yet another objective of the present invention is to provide a dilatation device that has a balloon that when inflated has a desired compliance and tensile strength to allow expansion in a controlled manner to a desired inflated diameter of the balloon.
A further objective of the present invention is to provide an easily constructed catheter balloon capable of unitary and integral construction having a uniform or near uniform outer diameter in order to provide relative ease of insertion into a blood vessel or body cavity.
Yet a further objective of the present invention is to provide a simple method for manufacturing dilatation devices having the characteristics listed above.